Barrier polymers are thoroughly discussed in "Encyclopedia of Science and Technology", 2nd Edition, Vol. 2 (Kirk-Othmer), pp. 176-192; 4th Edition, Vol. 3, pp. 931-962.
While plastics have found wide spread utility for containment of food and non-food products, they have often been found to be lacking in their barrier characteristics towards gases such as oxygen and carbon dioxide, or solvents such as gasoline, toluene, methylene chloride, or moisture.
The need for barrier properties towards oxygen, carbon dioxide, etc., is felt most importantly for the packaging of food. Oxidation of food due to the ambient oxygen can cause browning, rancidity, off-taste and off-smell, mold formation, etc., sometimes posing serious health hazards. A less serious yet commercially important problem is the loss of carbon dioxide from carbonated beverages, causing the beverage to go "flat".
While it is desirable to package a number of products, such as coffee or fruit juices in unbreakable, light weight or transparent plastic containers, such containers often absorb the essential oils and aroma components out of the product, resulting in an off-taste or smell, called distortion. The perfume, cologne, and cosmetic industry has also long recognized the same problem with respect to their packaging needs.
In non-food applications, there is a need for containment for fuels, gasoline additives, solvent-based cleaners, non-polar solvents, etc. and other active ingredients in polymer, particularly polyolefin, containers. The problem is further compounded by the problem of migration of unreacted monomers, low molecular weight polymers and other processing aids and additives from the container into the product; i.e., leaching. Such problems are particularly acute for containment of fuels in gasoline tanks and agricultural tanks, for protection of wire cables, and for waste containment with geomembranes.
Patented processes are known whereby the inner surface of plastic containers are modified by sulfonation or fluorination during or after the blow molding of the container. This treatment changes the surface characteristics of the polyolefin used to make the container so that the solvent is kept from wetting the inner surface. This prevents absorption and transmission of the solvent vapor through the container wall. The polyolefin is thus a barrier to either nonpolar solvents or aqueous solutions of active ingredient. Such containers can be used for herbicides, pesticides, gasoline, and other products that would normally penetrate polyolefin and would frequently be packaged in glass or metal.
For example, U.S. Pat. No. 3,862,284 discloses a process whereby the barrier properties of blow molded thermoplastic articles are improved by employing a blowing gas containing about 0.01 to about 20% by volume fluorine during the expansion of the thermoplastic article.
U.S. Pat. No. 4,515,836 discloses a process for providing a substrate such as poly(ethylene terephalate) container with a gas barrier coating of a copolymer of vinylidene chloride. The outside surface of the container is impacted with a stream of a stabilized aqueous polymer dispersion with sufficient force to cause selective destabilization of the dispersion at the surface interface to form a gel layer containing the polymer in the continuous phase. This gel layer serves as an adhesive layer for an overlaying layer of the aqueous polymer dispersion as a continuous uniform coating.
British Patent No. 2,069,870 B discloses a process for improving the barrier properties of polymeric containers, by treating at least one surface of the container with sulphur trioxide, followed by washing with an aqueous medium and subsequently applying a layer of a dispersion of a melamine-formaldehyde or urea-formaldehyde condensation product. The dispersion layer is then cured to form the final product.
Chemical vapor resistance and barrier property enhancement have been traditionally achieved commercially by surface treatment or coextrusion technologies. These approaches are further taught in U.S. Pat. Nos. 4,764,405,
Hitherto, approaches such as surface treatment or coextrusion have in some circumstances provided excellent improvements for various substrates.
Barrier polymers are often used in combination with other polymers or substances. The combinations may result in a layered structure either by coextrusion, lamination, or coating. The combinations may be blends that are either miscible or immiscible. In each case, the blend seeks to combine the best properties of two or more different materials to enhance the value of a final structure. An example of an immiscible blend is an inert filler in a polymer matrix.
Fluorochemical additives have demonstrated the unique ability to modify the surface properties of polymers and act as processing aids. Fluorochemicals inherently retain these unique migrating properties while maintaining the high molecular weight necessary to minimize volatility.
It has now been found that a variety of polymer substrates with increased chemical and vapor resistance and enhanced barrier properties are readily prepared by melt compounding the subject polymer fluoroelastomers, fluorochemicals or mixtures thereof, wherein said fluorochemical or fluoropolymer contains greater than 40% fluorine by weight and exhibits less than 20% weight loss at 165.degree. C., as measured by thermogravimetric analysis at 20.degree. C./minute in air. Said fluorochemicals or fluoropolymers can also act as processing aids or mold release agents and enhance other properties such as environmental crack resistance and long term light and heat stability.
The instant invention is particularly useful to improve the chemical and vapor resistance and barrier properties of pellicles, films, membranes, molded articles, containers and the like. In particular, it is useful in the production of gasoline tanks, agricultural tanks, wire cables and geomembranes.
The use of fluorochemicals for protective clothing made from polypropylene nonwoven fiber is described in a paper by D. R. Thompson et al., entitled "New Fluorochemicals for Protective Clothing" from Book-Pap.-Int. Nonwoven Fabric Conf. (1990) pp. 345-364.